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      1 /* Copyright (c) 2009, Google Inc.
      2  * All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions are
      6  * met:
      7  *
      8  *     * Redistributions of source code must retain the above copyright
      9  * notice, this list of conditions and the following disclaimer.
     10  *     * Redistributions in binary form must reproduce the above
     11  * copyright notice, this list of conditions and the following disclaimer
     12  * in the documentation and/or other materials provided with the
     13  * distribution.
     14  *     * Neither the name of Google Inc. nor the names of its
     15  * contributors may be used to endorse or promote products derived from
     16  * this software without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     29  *
     30  * ---
     31  * This file is a Linux-specific part of spinlock_internal.cc
     32  */
     33 
     34 #include <errno.h>
     35 #include <sched.h>
     36 #include <time.h>
     37 #include <limits.h>
     38 #include "base/linux_syscall_support.h"
     39 
     40 #define FUTEX_WAIT 0
     41 #define FUTEX_WAKE 1
     42 #define FUTEX_PRIVATE_FLAG 128
     43 
     44 // Note: Instead of making direct system calls that are inlined, we rely
     45 //       on the syscall() function in glibc to do the right thing. This
     46 //       is necessary to make the code compatible with the seccomp sandbox,
     47 //       which needs to be able to find and patch all places where system
     48 //       calls are made. Scanning through and patching glibc is fast, but
     49 //       doing so on the entire Chrome binary would be prohibitively
     50 //       expensive.
     51 //       This is a notable change from the upstream version of tcmalloc,
     52 //       which prefers direct system calls in order to improve compatibility
     53 //       with older toolchains and runtime libraries.
     54 
     55 static bool have_futex;
     56 static int futex_private_flag = FUTEX_PRIVATE_FLAG;
     57 
     58 namespace {
     59 static struct InitModule {
     60   InitModule() {
     61     int x = 0;
     62     // futexes are ints, so we can use them only when
     63     // that's the same size as the lockword_ in SpinLock.
     64 #ifdef __arm__
     65     // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
     66     have_futex = 0;
     67 #else
     68     have_futex = (sizeof (Atomic32) == sizeof (int) &&
     69                   syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
     70 #endif
     71     if (have_futex &&
     72         syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
     73       futex_private_flag = 0;
     74     }
     75   }
     76 } init_module;
     77 
     78 }  // anonymous namespace
     79 
     80 
     81 namespace base {
     82 namespace internal {
     83 
     84 void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
     85   if (loop != 0) {
     86     int save_errno = errno;
     87     struct timespec tm;
     88     tm.tv_sec = 0;
     89     if (have_futex) {
     90       // Wait between 0-16ms.
     91       tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
     92       // Note: since Unlock() is optimized to not do a compare-and-swap,
     93       // we can't expect explicit wake-ups. Therefore we shouldn't wait too
     94       // long here.
     95       syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
     96                 FUTEX_WAIT | futex_private_flag,
     97                 value, reinterpret_cast<struct kernel_timespec *>(&tm));
     98     } else {
     99       tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
    100       nanosleep(&tm, NULL);
    101     }
    102     errno = save_errno;
    103   }
    104 }
    105 
    106 void SpinLockWake(volatile Atomic32 *w, bool all) {
    107   if (have_futex) {
    108     syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
    109               FUTEX_WAKE | futex_private_flag, 1, 0);
    110   }
    111 }
    112 
    113 } // namespace internal
    114 } // namespace base
    115